1. Field of the Invention
The present invention relates to a fabrication method for a molybdenum disilicide (MoSi.sub.2) sintered body, and more particularly, to a low-temperature sintering method for a molybdenum disilicide powder in which molybdenum disilicide powder having an excellent oxidation resistance is molded at a low temperature and under no pressure so as to fabricate a high density sintered product.
2. Description of the Prior Art
Generally, since molybdenum disilicide has a high melting point (2030.degree. C.), a low density (6.3 g/cc) and excellent oxidation resistance, it is commonly referred to as super kanthal and is used as a high temperature heating element.
The reason that molybdenum disilicide has an excellent oxidation resistance characteristic is that silicon (Si), one of composing elements of the molybdenum disilicide, is combined with oxygen in air to form silica (SiO.sub.2) which is an oxidation-resistant layer on the surface of the sintered product, which prevents oxygen from being diffused to the inside of the material.
However, as reported in recent publication (Mat. Res. Soc. Symp. Proc. vol.322.1994), the sintering of a powder material is generally carried out at 1600.degree. which corresponds to about 80% of the melting point even when the average powder grading is about 1 micron, and several to tens of hours are disadvantageously required to carry out such process.
Since a fabrication process which requires a long time at a high temperature needs much energy, and causes an increase in the fabrication cost of the product, a hot pressing method has been adopted wherein heat and pressure are applied together to sinter a powder material within a short time at a low temperature.
However, such hot pressing method requires a separate apparatus, resulting in an increase in fabrication cost.
A representative example that has been studied to solve such problem is the method of mechanically mixing the powder or employing a milling process. In case of molybdenum disilicide, if powders of molybdenum and silicon are mechanically mixed, molded and heated, about 90% of the theoretical density can be obtained by combustion synthesis within one hour at the temperature range of 1400.about.1450.degree. C. under no pressure, according to one report disclosed in Mat. Res. Soc. Symp. Proc. vol.364.1995.
However, to utilize molybdenum disilicide as a high temperature material, its mechanical characteristics and oxidation resistance have yet to be estimated, and the powder materials must not be polluted by air since they are to be mixed or alloyed.